The conventional synthesis of bifunctional hydrocarbon-based compounds, such as unsaturated acids, unsaturated nitriles, acid anhydrides, acetals, aldehydes, epoxides including ethylene oxide and propylene oxide, is carried out industrially via chemical process using raw materials derived from fossil hydrocarbons.
The current change in terms of the environment results, in the energy and chemistry fields, in a preference for the exploitation of natural raw materials originating from a renewable source and also waste. It is the reason why work has been undertaken to industrially develop processes using as raw material products derived from biomass.
Among the conversion processes, fermentation, known for thousands of years and “institutionalized” by Pasteur, has a place of its own and is used only in well-defined industrial sectors; see in this respect the Techniques de l'Ingénieur [Techniques of the engineer] J 6 006, pages 1 to 18. The synthesis of “solvents” such as acetone, butanol and ethanol by fermentation of carbohydrates is well known, mention may particularly be made of U.S. Pat. No. 1,315,585, and has been used industrially since 1919 with a Clostridium acetobutylicum bacterium. It should be noted that a bacterium of this genus is used for the synthesis, by fermentation, of acids such as propionic acid, acetic acid and succinic acid (Techniques de l'Ingénieur [Techniques of the engineer] J 6 002, page 9, table 4). From the 1950s onwards, competition for these old processes arrived in the form of chemical processes using oil products, the cost of which was much lower.
In the remainder of the text,                the term “bifunctional hydrocarbon-based compounds” is intended to mean compounds with 2 to 6 carbon atoms per molecule comprising two functions, and the term “function” should be understood to mean acid, nitrile, aldehyde, ether or olefinic unsaturation functions. These bifunctional compounds are therefore, for example, diacids, acid anhydrides, unsaturated acids, unsaturated nitriles, unsaturated aldehydes, acetals, diols in the form of epoxide (or oxirane), such as ethylene oxide, propylene oxide, etc.,        the term “intermediate (fermentation) compounds” is intended to mean saturated acids, hydroxy acids, lactic acid, 3-hydroxypropionic acid, 3-hydroxybutyric acid, 2-hydroxyisobutyric acid, 3-hydroxyisobutyric acid, etc., α-olefins and alcohols,        the term “biomass” is intended to mean the biodegradable fraction of products, of waste as defined in European Directive No. 2003/30/EC of 8 May 2003 and which can be converted via fermentation in the presence of microorganisms such as enzymes, bacteria, yeasts, fungi, etc.        The term “biomass” will be intended to mean sugars, starches, celluloses and hemicellulose and any vegetable matter containing sugar, cellulose, hemicellulose and/or starch, and also the syngas.        
The vegetable matters containing sugars are mainly sugar cane and sugar beet; mention may also be made, for example, of maple, date palm, sugar palm, sorghum and American aloe.
The vegetable matters containing cellulose and/or hemicellulose are, for example, wood, straw, maize cobs, and seed or fruit oilcakes.
The vegetable matters containing starches are mainly cereals and legumes, wheat, maize, sorghum, rye, rice, potato, cassava, sweet potato, or else algae.
Among the matters derived from recovered materials, mention may be made of plant or organic waste containing sugars and/or starches and/or cellulose, and more generally any fermentable waste, including the syngas derived from natural or industrial processes, and carbon monoxide. The syngas which may be suitable for this type of fermentation can have an H2/CO molar ratio which varies in a broad range, in particular from 0/1 to 4/1.
The microorganisms used in bioconversion are also well known. These microorganisms depend on the type of biomass to be treated and on the selected mode of fermentation, which may be aerobic or anaerobic. By way of example, mention may be made of alcoholic fermentation with yeasts and bacteria of the Zymomonas or Zymosarcina genus; homolactic fermentation with bacteria of the Streptococcus or Lactobacillus genus, heterolactic fermentation with bacteria of the Leuconostoc or Lactobacillus genus, propionic fermentation with bacteria of the Clostridium, Propionibacterium or Corynebacterium genus, butyroacetonobutylic fermentation with bacteria of the Butyribacterium or Zymosarcina genus, mixed acid fermentation with bacteria of the Escherichia, Salmonella or Proteus genus, and butylene glycol fermentation with bacteria of the Aerobacter or Aeromonas genus, etc. More recent work has shown that it is possible to introduce improvements into the fermentation processes by successively using two different types of bacteria, which may belong to the same genus, for carrying out the two steps of the overall process, the intermediate step being the synthesis of the acid. In this respect, mention may be made of U.S. Pat. No. 5,753,474 which describes the synthesis of butanol and of similar compounds by fermentation of carbohydrates with bacteria of the Clostridium genus, such as C. tyrobutyricum, C. thermobutyricum, C. butyricum, C. cadaveros, C. cellobioparum, etc. (column 3, lines 1 to 17). Moreover, even more recent work has shown that it is possible to introduce into certain microorganisms, either by integration within the cell, or by complementary external provision, additional functions capable of improving selectivity and even of allowing new conversions. In this respect, mention may be made of the patent (PCT/FR2009/051332) which describes the synthesis, by fermentation, of terminal alkenes from a carbon source (biomass) by means of a microorganism capable of converting the carbon source into compounds of 3-hydroxyalkanoate type, said microorganism being associated with an enzyme of decarboxylase type which makes it possible to decarboxylate the 3-hydroxyalkanoates formed.
The gas-phase chemical oxidation of olefins, alcohols or acids or aldehydes which are saturated (oxydehydrogenation of alcohols, acids and aldehydes) is also well known.
In the current gas-phase oxidation processes, the compound to be oxidized (alcohol, acid or aldehyde which is saturated, hydrocarbon, etc.) is generally brought into contact with air, very commonly air diluted with nitrogen, in an oxidation reactor. The implementation of this very exothermic reaction is technologically difficult and requires the use of multitubular reactors or fluidized-bed reactors.
Another constraint hangs over oxygen-oxidation reactors, said constraint being linked to the flammability range and therefore to the safety of the processes. It is desirable to be able to operate the reactors outside the flammability zone of the mixtures, for obvious reasons of safety. Unfortunately, this condition limits the operating range, since it is not possible to use large amounts of oxygen or of reagent to be oxidized, in an air-nitrogen-hydrocarbon or air-nitrogen-alcohol ternary mixture, for example.
The solutions usually implemented for avoiding the flammability range consists in diluting the reaction gases either with water vapour, or with recycling gases which are oxygen-depleted (and therefore nitrogen-rich).
It is also known practice to carry out oxidation reactions in the presence of a gas which is inert with respect to the reaction, such as COD, methane, or even propane. The applicant has, in this field, filed two patent applications regarding the partial oxidation, in the gas phase, of light alcohols (C1-C4), methanol in particular, in the presence of a C1-C5 hydrocarbon, methane in particular, for obtaining acetals (WO 07/128941) or light aldehydes (WO 08/007014).
Moreover, it has filed, jointly with the company Air Liquide, a French patent application No. 09 57731 of 2 Nov. 2009 relating to the oxidation of alkenes and in particular of propylene in the presence of propane, published under number WO 11/051621.
In these various cases, both methane and propane acted as a diluent (flammability range) and as a “thermal ballast” (elimination of heat). There are many advantages to adding these types of gases. They have a higher specific heat than nitrogen, they therefore transport more heat from the reactor, they are chemically inert and some inhibit free-radical combustion reactions better, which makes it possible to notably reduce the flammable mixture range and therefore to increase the operating range. The use of a gas ballast of this type therefore makes it possible to increase reactor productivity and/or selectivity. Unfortunately, gases such as methane, CO2 or propane are not already readily available on industrial sites, and their use requires complex recycling/purification processes. In addition, if CO2 was to be specifically produced, from fossil resources, it would contribute to increasing the anthropogenic fossil CO2 emissions of the industrial site, whereas the intention is to limit them.